1. Field of the Invention
This invention relates to a magnetic position sensor, and, according to a variant, a magnetic position and speed sensor.
2. Discussion of the Background
Position sensors using Hall probes detecting the magnetic flux generated by a magnet by relative movement relative to the Hall probe are known in the prior art. In particular, French patent 2624966 describes a coder for a print wheel comprising a Hall-effect linear detector and a permanent magnet mounted in a nonferrous metal shaft exhibiting a ring forming a conductive flux spiral molded in the wheel and encircling the shaft. The angular position of the print wheel is determined in absolute value by the amplitude of the signal relative to the transition point of the spiral. In another embodiment, a second Hall-effect detector is placed on the shaft, being opposite to the first detector to provide a reinforced signal.
The sensors thus produced do not exhibit a signal which is actually linear, and, in the prior art, this drawback has been remedied by digitizing the signal delivered by the Hall probe and by processing the signal by data-processing means.
It has also been proposed in the prior art to remedy the defect of linearity of magnetic position sensors by complex geometries. During the European colloquium on the "modern magnets and new machines with magnets" which was held in Grenoble on Jun. 13 to 15, 1990, a position sensor delivering an output signal approximately proportional to the angular position was exhibited. This sensor comprised a magnetized ring of elliptical shape according to a first embodiment, or an original qualified geometry consisting of two arcs of a circle. The linearity error is thus cancelled by the eccentricity. If, on the theoretical plane, this solution is advantageous, it is technically difficult to achieve for sensors produced industrially in large scale. The production cost is thereby excessive for many applications.